1. Field of the Invention
The present invention relates to methods of detecting the surface and/or subterranean locations of well treating fluids, and more particularly, to methods of detecting the location of such a fluid after the fluid has been introduced into a well and used for performing a treatment therein.
2. Description of the Prior Art
A variety of well treatments using treating fluids are performed in the completion and stimulation of oil and gas wells. For example, cementing treatments are carried out in the construction and repair of wells utilizing a cement composition as the treating fluid. In forming a cement composition, a hydraulic cement is normally mixed with water and other additives to form a pumpable cement composition which is placed in a subterranean zone penetrated by a well bore. After placement in the zone, the cement composition sets into a hard substantially impermeable mass in the zone.
High viscosity well treating fluids are also utilized in the construction of a well and in the stimulation of formations penetrated by the well bore to enhance the production of oil and gas therefrom. The most commonly used such treating fluids are high viscosity gelled fluids which are utilized in completion treatments such as in forming gravel packs and stimulation treatments such as hydraulic fracturing.
The most common cementing treatment or operation performed in the construction of a well is primary cementing whereby a metal pipe string such as casing or a liner is placed in the well bore and bonded therein by cement. Other cementing treatments utilized in wells are usually remedial in nature. For example, a cement composition is often squeezed into cracks or openings in pipe disposed in the well bore, in the cement sheath in the annulus between the pipe and the well bore, and in other similar locations and allowed to set therein whereby the cracks or openings are plugged.
An example of a stimulation procedure which is performed using a high viscosity treating fluid is hydraulic fracturing. Hydraulic fracturing is performed by injecting a high viscosity fluid through the well bore into a subterranean formation to be fractured and applying sufficient fluid pressure on the formation to cause its breakdown and the production of one or more fractures therein. A fracture proppant material such as sand or other particulate material is usually suspended in the high viscosity fracturing fluid whereby the proppant material is carried into the fractures and deposited therein. When pressure on the fractured formation is released, the fractures are propped open by the proppant material therein.
In all of the various completion and stimulation treatments where a treating fluid is introduced into a subterranean zone penetrated by a well bore, it is difficult to confirm that the treating fluid utilized has entered and/or filled the desired subterranean zone. As a result, methods of detecting the locations of a well treating fluid after it has been introduced into a well have heretofore been developed and used. Typically, a radioactive tracer material is included in the treating fluid and after the placement of the treating fluid containing the radioactive tracer, an instrument which detects radioactivity is lowered in the well and utilized to determine the location or locations of the treating fluid.
The monitoring of produced well fluids on the surface to ascertain the presence of a treatment fluid containing a tracer material previously injected into a well would be a valuable tool in determining the life and/or quality of the treatment. For example, wells are often chemically treated to prevent the formation of scale in the producing formation and related equipment. By detecting the concentration of the chemical in produced fluids, the duration of the treatment and the optimum time for repeating the treatment could be determined. However, if radioactive tracer material was used in such an application, the produced fluids containing the radioactive material would be contaminated and unsafe.
Radioactive tracers are expensive and are considered hazardous whereby they and the fluids containing them must be handled and disposed of in accordance with the laws and rules relating to hazardous materials. Thus, there is a need for an improved method of detecting the location of a well treating fluid after the treating fluid has been introduced into a well and used for performing a treatment therein which does not involve the use of radioactive tracer materials or other hazardous materials which must be disposed of in a special manner.